Lead plate with a joint portion having a surface area smaller than that of its mounting portion

ABSTRACT

A lead plate for connecting a printed circuit board (PCB) of a secondary battery to an bare cell includes a mounting portion connected to the PCB, a joint portion connected to the bare cell, a surface area of the joint portion facing the bare cell being smaller than a surface area of the mounting portion facing the PCB, and a step portion connecting the mounting portion and the joint portion to each other.

BACKGROUND

1. Field

Example embodiments relate to a lead plate of a secondary battery and aprotection circuit module having the same. More particularly, exampleembodiments relate to a lead plate and a protection circuit modulehaving the same, which can enhance the performance and reliability of asecondary battery by improving the assembled structure of the secondarybattery.

2. Description of the Related Art

A secondary battery is a battery that can be repeatedly charged anddischarged. Secondary batteries may be classified into nickel-cadmium(Ni—Cd) secondary batteries, nickel-hydrogen (Ni-MH) secondarybatteries, lithium secondary batteries, and the like. For example,lithium secondary batteries may be divided into lithium ion secondarybatteries using a liquid electrolyte and lithium polymer secondarybatteries using a polymer electrolyte, depending on the kind ofelectrolyte used. In addition, the lithium secondary batteries may bedivided into a prismatic type, a cylinder type, a pouch type, and thelike, depending on their shapes.

A battery pack using a lithium secondary battery may typically include abare cell and a protection circuit module. The bare cell refers to abasic structure of the battery, including an electrode assembly, anelectrolyte, and an outer case in which the electrode assembly and theelectrolyte are accommodated. The protection circuit module (PCM)protects the bare cell from overcharge or overdischarge when the barecell is charged or discharged.

SUMMARY

Embodiments are therefore directed to a lead plate of a secondarybattery and a protection circuit module, which substantially overcomeone or more of the problems due to the limitations and disadvantages ofthe related art.

It is therefore a feature of an embodiment to provide a lead platehaving a structure capable of enhancing a joint strength between aprotection circuit module and a bare cell.

It is therefore another feature of an embodiment to provide a protectioncircuit module having the aforementioned lead plate, which canfacilitate a laser soldering process, reduce failures in a joiningprocess, and enhance reliability of a battery.

At least one of the above and other features and advantages may berealized by providing a lead plate for connecting a printed circuitboard (PCB) of a secondary battery to an bare cell, the lead plateincluding a mounting portion connected to the PCB, a joint portionconnected to the bare cell, a surface area of the joint portion facingthe bare cell being smaller than a surface area of the mounting portionfacing the PCB, and a step portion connecting the mounting portion andthe joint portion to each other.

In one embodiment, the mounting portion is divided into a contact regionat which it comes in contact with one surface of the protection circuitmodule and a non-contact region, and the area of the contact region isformed smaller than that of the joint portion connected to the barecell.

In one embodiment, the boundary portion between the mounting portion andthe step portion and the boundary portion between the step portion andthe joint portion are bent, and a notch is formed in at least one regionof the bending portion between the mounting portion and the step portionand the bending portion between the step portion and the joint portion.

The thickness of at least one portion of the mounting portion may begreater than that of the joint portion.

The non-contact region of the mounting portion may be formed to extendoutward from at least one surface of the contact region.

The width of the mounting portion may be wider than that of the jointportion.

In one embodiment, the mounting portion has a notch, and the jointportion has a punch or opening.

The non-contact region may have a wing portion bent and extended outwardfrom the contact region. The length of the wing portion extended fromthe mounting portion may be shorter than that of the step portionextended between the mounting portion and the joint portion.Alternatively, the width of the wing portion may be decreased in thedirection extending outward from the mounting portion so that the wingportion is spaced apart from the step portion at a predeterminedinterval.

At least one of the above and other features and advantages may also berealized by providing a protection circuit module including a PCB, asafety element and an external connection terminal, mounted on the PCB,and a lead plate joined with the PCB, wherein the lead plate includes amounting portion connected to one surface of the PCB, a joint portionconnected to the bare cell, and a step portion for connecting themounting portion and the step portion to each other, wherein the area ofthe mounting portion is formed larger than that of the joint portionjoined with the bare cell.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages will become more apparent tothose of ordinary skill in the art by describing in detail exemplaryembodiments with reference to the attached drawings, in which:

FIG. 1A illustrates a schematic perspective view of a protection circuitmodule according to an embodiment;

FIG. 1B illustrates a side view of the protection circuit module of FIG.1A;

FIG. 2A illustrates a schematic, enlarged side view of a lead plateaccording to an embodiment;

FIG. 2B illustrates a side view of a base material of the lead plate ofFIG. 2A;

FIG. 2C illustrates a plan view of the base material of FIG. 2B;

FIG. 3 illustrates a side view of a joined state of the lead plate ofFIG. 2A;

FIG. 4 illustrates a plan view of a base material of a lead plateaccording to another embodiment;

FIG. 5 illustrates a side view of a base material of a lead plateaccording to still another embodiment;

FIG. 6 illustrates a plan view of a base material of a lead plateaccording to still another embodiment;

FIG. 7 illustrates a plan view of a base material of a lead plateaccording to still another embodiment;

FIG. 8A illustrates a plan view of a base material of a lead plateaccording to still another embodiment;

FIG. 8B illustrates a perspective view of the lead plate made of thebase material of FIG. 8A;

FIG. 9A illustrates a plan view of a base material of a lead plateaccording to still another embodiment;

FIG. 9B illustrates a perspective view of the lead plate made of thebase material of FIG. 9A;

FIG. 10A illustrates a plan view of a base material of a lead plateaccording to still another embodiment;

FIG. 10B illustrates a perspective view of the lead plate made of thebase material of FIG. 10A; and

FIGS. 11A and 11B illustrate perspective, sequential views of processesin a method of manufacturing a battery pack according to an embodiment.

DETAILED DESCRIPTION

Korean Patent Application No. 10-2009-0126076, filed on Dec. 17, 2009,in the Korean Intellectual Property Office, and entitled: “Lead Plateand Protection Circuit Module Having the Same,” is incorporated byreference herein in its entirety.

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

In the drawing figures, the dimensions of elements and regions may beexaggerated for clarity of illustration. It will also be understood thatwhen a layer or element is referred to as being “on” another element orsubstrate, it can be directly on the other element or substrate, orintervening elements may also be present. In addition, it will also beunderstood that when an element is referred to as being “between” twoelements, it can be the only element between the two elements, or one ormore intervening elements may also be present. Like reference numeralsrefer to like elements throughout.

FIG. 1A illustrates a schematic perspective view of a protection circuitmodule according to an embodiment, and FIG. 1B illustrates a schematicside view of the protection circuit module of FIG. 1A. Referring toFIGS. 1A and 1B, the protection circuit module 10 may include asubstrate 20, safety elements 32 and 34 on the substrate 20, an externalconnection terminal 40 on the substrate 20, and a lead plate 50connected to the substrate 20.

The substrate 20 may include a printed circuit board (PCB) havinginterconnection patterns formed therein. For example, the substrate 20(may be referred hereinafter as a “PCB”) may have a shape of a platehaving a length that is a few times or a few tens of time longer thanits width or thickness. As illustrated in FIG. 1, the substrate 20 maybe provided with a hole 22 passing through an approximate center portionthereof. When the protection circuit module 10 is joined with a barecell, the hole 22 may be used as a passage through which a welding rodmay be inserted to weld an electrode terminal (see 120 of FIG. 11A) ofthe bare cell and an electrode terminal, e.g., a second terminal 35 b inFIG. 1B, of the safety element 34.

The safety elements 32 and 34 may refer to a protection module 32 and atemperature sensor 34. The safety elements 32 and 34 may be mounted on afirst surface, i.e., a bottom surface, of the substrate 20. Theprotection module 32 may control the charge/discharge operation of abattery pack for which the protection circuit module 10 is used, and mayprotect the battery pack from overcharge, overdischarge, overcurrent,and the like. The temperature sensor 34 may include a positivetemperature coefficient (PTC) thermistor. The temperature sensor 34 maybe connected to the protection module 32 through a first terminal 35 a,and may be connected to the electrode terminal (see 120 of FIG. 11A) ofthe bare cell through the second terminal 35 b.

The external connection terminal 40 may be on a second surface of thesubstrate 20, i.e., on a surface opposite the first surface, and mayform a current path between the bare cell and an external system, e.g.,a load, charging system or the like, after the protection circuit module10 is connected to the bare cell. The external connection terminal 40may include at least two or more terminals including positive andnegative terminals respectively connected to positive and negativeelectrodes of the bare cell. The external connection terminal 40 may bemounted on the second surface, i.e., a top surface, of the substrate 20.

The lead plate 50 may include a mounting portion mounted on a bottomsurface of the substrate 20, a joint portion 54 welded to an bare cell,e.g., a bare cell, and a step portion 56 for connecting the mountingportion 52 and the joint portion 54 to each other, so that a step may beformed between the bare cell and the protection circuit module 10. In anembodiment, when the protection circuit module 10 is welded to the barecell, the lead plate 50 may be formed to have a proper strength orelasticity for correcting a margin that may occur during themanufacturing process of the battery pack, e.g., a margin of the lengthof the bare cell, or the like.

In an embodiment, an area of the mounting portion 52 facing theprotection circuit module 10 may be larger than an area of the jointportion 54 facing the bare cell, e.g., the bare cell, so that a weightof the mounting portion 52 in the lead plate 50 may be greater than thatof the joint portion 54. Accordingly, it may be possible to prevent oneside of the joint portion 54 from being inclined or lifted, e.g.,separated, away from the bare cell, when a compression force is appliedto join the protection circuit module 10 with the bare cell.

In contrast, if a joint portion 54 is inclined away from the surface ofthe bare cell to be welded, a hole may be produced by laser in thejoining process, e.g., a laser welding, or the joint portion 54 may notbe appropriately welded to the surface of the bare cell. As such, if thewelding is performed in the state that one side of the joint portion 54is inclined or lifted with respect to the surface of the bare cell, itmay be difficult to ensure a welding strength.

In an embodiment, one end portion of the lead plate 50 may be formed ina curved shape, e.g., the joint portion 54 may be curved as illustratedin FIG. 2C. However, other geometrical configurations of the lead plate50 are not excluded from example embodiments, e.g., an end portion ofthe lead plate 50 may have a rectangular shape such as a surface of arectangular parallelepiped.

The protection circuit module 10 may have a pair of lead plates 50 atboth ends in the length direction thereof. Alternatively, the protectioncircuit module 10 may have a dummy plate 51 at any one of both the ends.The dummy plate 51 may be identical to the lead plate 50, except thatthe dummy plate 51 may not be used as a current path through which theprotection circuit module 10 is connected to the bare cell, e.g., whenthe protection circuit module 10 is used in a battery pack.

Hereinafter, the lead plate 50 will be described in more detail withreference to FIGS. 2A-2C. FIG. 2A illustrates a side view of the leadplate 50 according to an embodiment, FIG. 2B illustrates a side view ofa base material of the lead plate of 50, and FIG. 2C illustrates a planview of the base material of FIG. 2B.

Referring to FIG. 2A, the lead plate 50 may include the mounting portion52 having a first length L1, the joint portion 54 having a second lengthL2, and the step portion 56 having a third length L3 to connect themounting portion 52 and the joint portion 54 to each other in onedirection. In this embodiment, the first length L1 may be longer thanthe second length L2.

The mounting portion 52 corresponds to a portion of the lead plate 50that is joined with the substrate 20, e.g., through a reflow solderingprocess. The joint portion 54 corresponds to a portion of the lead plate50 that contacts the bare cell when the protection circuit module 10having the lead plate 50 is joined with the bare cell, e.g., by welding.The step portion 56 corresponds to a portion of the lead plate 50 thatconnects the mounting portion 52 and the joint portion 54. The stepportion 56 may form a step with a predetermined height between the barecell and the protection circuit module 10, when the protection circuitmodule 10 is joined with the bare cell. The step formed by the stepportion 56 between the bare cell and the protection circuit module 10may provide a space for forming the safety elements 32 and 34 on theprotection circuit module 10.

The lead plate 50 may be formed by bending a conductive or metallicplate. For example, the conductive/metallic plate may be formed ofnickel or a nickel alloy. For example, as illustrated in FIG. 2B, aconductive or metallic plate having an initial linear, flat structuremay be bent twice in different directions from the length direction inorder to form the lead plate 50 in FIG. 2A. In other words, theconductive/metallic plate in FIG. 2B may be bent twice in order to formthe mounting portion 52 and the joint portion 54 that are bentrelatively to the step portion 56 of the lead plate 50 in FIG. 2A. Asillustrated in FIG. 2B, the metallic plate may have a substantiallyuniform thickness t1 and a length (L1+L2+L3). Further, as illustrated inFIG. 2C, the metallic plate may have a width W1. If the lead plate 50 isformed by bending the metallic plate twice in different directions, itmay have a step shape. Thus, in the state that the mounting portion 52is joined with the substrate 20, the joint portion 54 may be welded tothe bare cell, e.g., to an external surface of a bare cell extendingalong a length direction of the substrate 20.

As further illustrated in FIG. 2A, the joint portion 54 of the leadplate 50 may be bent outward (left in the figure) at an obtuse anglewith respect to the step portion 56. That is, the joint portion 54 maybe positioned at a predetermined angle θ1 with respect to a normal tothe step portion 56, so an angle between the step portion 56 and thejoint portion 54 may be larger than a right angle by the predeterminedangle θ1, i.e., an angle between the joint portion 54 and an extensionof the step portion 56 may be smaller than a right angle by thepredetermined angle θ1. The mounting portion 52 may be bent inward(right in the figure) to be approximately perpendicular to the stepportion 56. According to such bent angles, when the mounting portion 52is joined with the protection circuit module 10, as illustrated in FIGS.1A and 1B, the joint portion 54 may be bent away from the protectioncircuit module 10, e.g., extend in the direction of about 8 o'clockwhile being inclined by the angle θ1 in the extension direction of themounting portion 52.

According to this embodiment, the area at which the mounting portion 52is connected to the protection circuit module 10 may be larger than thearea at which the joint portion 54 is connected to the bare cell, sothat the weight of the mounting portion 52 may be greater than that ofthe joint portion 54. In other words, the mounting portion 52 and thejoint portion 54 may be formed of a same material and have asubstantially same width and thickness, so the mounting portion 52 maybe heavier than the joint portion 54 due to the larger length L1 of themounting portion 52. Thus, when the protection circuit module 10 havingthe lead plate 50 is welded to the bare cell, it may be possible toprevent one side of the joint portion 54 from being inclined or liftedwith respect to the joint surface. That is, weldability may be improvedby using the lead plate 50 of this embodiment.

FIG. 3 illustrates a side view of a joined state of the lead plate 50.When the protection circuit module 10 is joined with an bare cell, e.g.,a bare cell 100, via the lead plate 50, the lead plate 50 may becompressed with a predetermined pressure on one surface of the bare cell100 to weld the lead plate 50 to the bare cell 100. In detail, themounting portion 52 of the lead plate 50 may be previously attached tothe protection circuit module 10, e.g., an entire surface of themounting portion 52 facing the substrate 20 of the protection circuitmodule 10 may be in direct contact therewith. Further, pressure may beapplied to an interface between the joint portion 54 of the lead plate50 and the bare cell 100, so the joint portion 54 may be attachedparallel to the surface of the bare cell 100, as illustrated in FIG. 3.

That is, in the joint state of the lead plate 50 according to exampleembodiments, the mounting portion 52 may be joined parallel to onesurface of the protection circuit module 10, and the joint portion 54may be welded to the bare cell 100 by being attached parallel to thesurface of the bare cell 100. Further, the step portion 56 may be formedto connect in the vertical direction between the mounting portion 52 andthe joint portion 54, which extend parallel to each other, i.e., in thejoined state. The joint state exhibits excellent reliability in the droptest of the battery pack.

In contrast, when a protection circuit module is welded to a bare cellby using a conventional lead plate, e.g., a lead plate including a jointportion that is longer than a mounting portion, the weight of the longerjoint portion may be larger than that of the shorter mounting portion.As such, an edge of the longer joint portion may be inclined away fromthe bare cell, so weldability of the conventional lead plate to the barecell 100 may be poor due to the larger weight of the joint portion. Inother words, if the weight of the joint portion is greater than that ofthe mounting portion, a centroid, i.e., a center of mass, of the leadplate may be positioned at a boundary between the joint portion and astep portion. Therefore, when a force is applied to the boundary portionbetween the joint portion and the step portion, i.e., one end portion ofthe joint portion, in the length direction of the step portion duringwelding, the other end portion of the joint portion may be lifted to apredetermined height from the surface of the bare cell due to thestrength or elasticity of the joint portion itself. In this case, whenthe conventional lead plate is joined with the bare cell 100 by a laserwelding method, a hole may be produced in the joint portion of the leadplate, or the welding may not be properly performed. Therefore, awelding failure may easily occur.

Therefore, in the lead plate 50 according to example embodiments, thearea of the mounting portion 52 facing the protection circuit module 10may be larger than that of the joint portion 54, so that the weight ofthe mounting portion 52 may be greater than that of the joint portion54. In this case, a center of mass of the lead plate 50 may bepositioned between the boundary portion of the mounting portion 52 andthe step portion 56, i.e., one end portion of the mounting portion 52,and the other end portion of the mounting portion 52. Thus, when acompression force is applied in the length direction of the step portion56 when the lead plate 50 is welded to the bare cell 100, thecompression force applied to one end portion of the joint portion 54 isdistributed over the entire joint portion 54, as the center of mass ispositioned on the mounting portion 52. Accordingly, it may be possibleto prevent the other portion of the joint portion 54 from beinginclined.

In the following embodiments, various shapes of lead plates will bedescribed. For convenience of illustration, in some embodiments, a basematerial of a lead plate is referred to as a lead plate manufactured bythe base material, and is designated by reference numeral (one of 50 ato 50 g).

FIG. 4 illustrates a plan view of a base material of a lead plateaccording to another embodiment. Referring to FIG. 4, a lead plate 50 amay include a mounting portion 52 a having a first length L1, a jointportion 54 a having a second length L2, a step portion 56 a having athird length L3 to connect the mounting portion 52 a and the jointportion 54 a to each other, and at least one notch, e.g., first notch 58a and/or second 58 b. In this embodiment, the width and thickness of thelead plate 50 a may be constant, and the first length L1 may be longerthan the second length L2.

In detail, the first notch 58 a may be positioned at one end or bothends in the width direction of the base material of the lead plate 50 a,i.e., on a boundary portion (or first bending portion) of the mountingportion 52 a and the step portion 56 a. The second notch 58 b may bepositioned at one end or both ends in the width direction of the basematerial of the lead plate 50 a on a boundary portion (or second bendingportion) of the joint portion 54 a and the step portion 56 a. The firstnotch 58 a may facilitate the bending of the mounting portion 52 a andthe step portion 56 a, and the second notch 58 b may facilitate thebending of the joint portion 54 a and the step portion 56 a.

FIG. 5 illustrates a side view of a base material of a lead plateaccording to still another embodiment. Referring to FIG. 5, a lead plate50 b may include a mounting portion 52 b having a first length L1 a, thejoint portion 54 having the second length L2, and the step portion 56having the third length L3 to connect to the mounting portion 52 b andthe joint portion 54 to each other. The mounting portion 52 b may have anon-uniform thickness, so a first portion having a first thickness t1may be thinner than a second portion having a second thickness t2. It isnoted that thicknesses of the joint portion 54 and step portion 56 maybe substantially uniform, and may have the first thickness t1. In thisembodiment, when assuming that the width of the lead plate 50 b isconstant and the first and second lengths L1 a and L2 are identical toeach other, the weight of the mounting portion 52 b may be greater thanthat of the joint portion 54 due to the different thicknesses of themounting portion 52 b. In other words, according to this embodiment, alarger thickness of the mounting portion 52 b may be used, so that theweight of the mounting portion 52 b may be greater than that of thejoint portion 54.

FIG. 6 illustrates a plan view of a base material of a lead plateaccording to still another embodiment. Referring to FIG. 6, a lead plate50 c may include a mounting portion 52 c having the first length L1 a, ajoint portion 54 a having the second length L2, and the step portion 56having the third length L3 to connect the mounting portion 52 c and thejoint portion 54 a to each other. The joint portion 54 a may have anopening 55 c, i.e., a portion of the joint portion 54 a may be removed.In this embodiment, when assuming that the width of the lead plate 50 cis constant and the first and second lengths L1 a and L2 are identicalto each other, the weight of the mounting portion 52 c may be greaterthan that of the joint portion 54 a due to the opening 55 c. In otherwords, a contact area of the mounting portion 52 c with the protectioncircuit module 10 may be larger than the area of the joint portion 54 aby forming the opening 55 c.

According to this embodiment, the opening 55 c of the joint portion 54 amay be used, so that the weight of the mounting portion 52 c may begreater than that of the joint portion 54 a. It will be apparent thatthe shape and the position of the opening 55 c may be arbitrarilycontrolled considering the welding point of the joint portion 54 a.

FIG. 7 illustrates a plan view of a base material of a lead plateaccording to still another embodiment. Referring to FIG. 7, a lead plate50 d may include a mounting portion 52 d having a first length L1 b, thejoint portion 54 having the second length L2, and the step portion 56having the third length L3 to connect the mounting portion 52 d and thejoint portion 54. A width W2 of the mounting portion 52 d may be widerthan the width W1 of the joint portion 54. In this embodiment, whenassuming that the thickness of the lead plate 50 is substantiallyconstant and the first and second lengths L1 b and L2 are identical toeach other, the weight of the mounting portion 52 d may be greater thanthat of the joint portion 54 due to the width difference. In otherwords, according to this embodiment, the width of the mounting portion52 d, which is wider than that of the joint portion 54, may be used sothat the weight of the mounting portion 52 d may be greater than that ofthe joint portion 54.

When the width of the mounting portion 52 d is wider than that of thejoint portion 54, a portion extending outward from the protectioncircuit module 10 may not contact the protection circuit module 10.Here, the mounting portion 52 d may be divided into a contact region atwhich it comes in contact with the protection circuit module 10 and anon-contact region at which it does not come in contact with theprotection circuit module 10.

Although an area of the contact region of the mounting portion 52 d withthe protection circuit module 10 may be the same as or smaller than thatof the joint portion 54, an entire area of the mounting portion 52 d maybe larger than that of the joint portion 54. Therefore, the weight ofthe mounting portion 52 d may be greater than that of the joint portion54. That is, in this embodiment, when the mounting portion 52 d isdivided into a contact region at which it comes in contact with theprotection circuit module 10 and a non-contact region that is extendedoutward from the protection circuit module 10 and not coming in contactwith the protection circuit module 10, the contact area of the mountingportion 52 d may be the same as or smaller than that of the jointportion 54. For example, the area of the contact region of the mountingportion 52 d may be relatively smaller than that of the joint portion54, thereby preventing problems, e.g., welding failures. Further, thenon-contact region of the mounting portion 52 d may be formed so thatthe entire area of the mounting portion 52 d is larger than that of thejoint portion 54, i.e., so that the weight of the mounting portion 52 dis greater than that of the joint portion 54, thereby enhancing thejoint strength of the protection circuit module 10. Thus, thereliability of the battery pack may be enhanced. In this embodiment,assuming that the weight of the mounting portion 52 d is greater thanthat of the joint portion 54, the first length L1 b may be formedslightly shorter than the second length L2.

FIG. 8A illustrates a plan view of a base material of a lead plateaccording to still another embodiment. FIG. 8B illustrates a perspectiveview of the lead plate made of the base material of FIG. 8A.

Referring to FIGS. 8A and 8B, a lead plate 50 e may include a mountingportion 52 e having a first length L1 b, the joint portion 54 having thesecond length L2, and the step portion 56 having the third length L3 toconnect the mounting portion 52 e and the joint portion 54 to eachother. The width W2 of the mounting portion 52 e may be wider than thewidth W1 of the joint portion 54. The mounting portion 52 e may have atleast one notch 53 e positioned at one end or both ends in the widthdirection of the lead plate 50 e. In this embodiment, when assuming thatthe thickness of the lead plate 50 e is substantially constant, and thefirst and second lengths L1 b and L2 are identical to each other, theentire area of the mounting portion 52 e may be larger than that of thejoint portion 54, and therefore, the weight of the mounting portion 52 emay be different from that of the joint portion 54.

The notch 53 e may be provided to enhance the joining of the mountingportion 52 e. That is, when the mounting portion 52 e is joined with theprotection circuit module 10 by a reflow soldering method, the notch 53e may increase the tension of the mounting portion 52 e so that the leadplate 50 e can be well welded to the protection circuit module.

FIG. 9A illustrates a plan view of a base material of a lead plateaccording to still another embodiment. FIG. 9B illustrates a perspectiveview of the lead plate made of the base material of FIG. 9A.

Referring to FIGS. 9A and 9B, a lead plate 50 f may include a mountingportion 52 f having a first length L4, the joint portion 54 having thesecond length L2, and the step portion 56 having the third length L3 toconnect the mounting portion 52 f and the joint portion 54 to eachother. The lead plate 50 f may also include a wing portion 53 f having afourth length L5 in the length direction and a fifth length L6 in thewidth direction of the mounting portion 52 f. As described previously,the wing portion 53 f may be a non-contact region bent to extend outwardfrom a contact region at which the mounting portion 52 f comes incontact with the protection circuit module 10 in the entire area of themounting portion 52 f.

The wing portion 53 f may be folded once in the folded direction of thestep portion 56 from one end of the mounting portion 52 f, and the fifthlength L6 may be formed shorter than the third length L3 of the stepportion 56. The fourth length L5 of the wing portion 53 f may beidentical to or slightly shorter than the first length L4 of themounting portion 52 f. Since the wing portion 53 f is connected only tothe mounting portion 52 f, it may function to increase the weight of themounting portion 52 f.

In this embodiment, the weight of the mounting portion 52 f connected tothe wing portion 53 f may be greater than that of the joint portion 54,even when the thickness of the lead plate 50 f is substantially constantand the first length L4 is identical to or slightly shorter than thesecond length L2. Further, in this embodiment, it may be possible toprevent the lead plate 50 f from being collapsed by the wing portion 53f of the lead plate 50 f, even when an impact is applied to a cornerportion of the battery pack in the drop test of the battery pack, inwhich the bare cell and the protection circuit module are joinedtogether using the lead plate 50 f.

FIG. 10A illustrates a plan view of a base material of a lead plateaccording to still another embodiment. FIG. 10B illustrates aperspective view of the lead plate made of the base material of FIG.10A.

Referring to FIGS. 10A and 10B, a lead plate 50 g may include a mountingportion 52 g having the first length L4, the joint portion 54 having thesecond length L2, and the step portion 56 having the third length L3 toconnect the mounting portion 52 g and the joint portion 54 to eachother. The lead plate 50 g may also include a wing portion 53 g having asixth length L7 in the length direction and the fifth length L6 in thewidth direction of the mounting portion 52 g.

Since the wing portion 53 g is connected only to the mounting portion 52g, it may function to increase the weight of the mounting portion 52 g.In this embodiment, the weight of the mounting portion 52 connected tothe wing portion 53 g may be greater than that of the joint portion 54,even when the thickness of the lead plate 50 g is substantially constantand the first length L4 is identical to or slightly shorter than thesecond length L2 so that the entire area is changed.

The wing portion 53 g may be folded once in the folded direction of thestep portion 56 from one end of the mounting portion 52 g, and the fifthlength L6 of the wing portion 53 g may be formed shorter than the thirdlength L3 of the step portion 56. The wing portion 53 g may have a slopeportion 59 formed at the side adjacent to the step portion 56. The slopeportion 59 may be formed so that the length of the wing portion 53 g inthe length direction of the lead plate 50 g is decreased from the lengthidentical to or slightly shorter than the first length L4 of themounting portion 52 g to the sixth length L7, while extending in thewidth direction of the lead plate 50 g from the mounting portion 52 g.

When the bending portion of the joint portion 54 and the step portion 56is folded at an acute angle, i.e., smaller than 90 degrees, because acompression force applied to the lead plate is slightly large when theprotection circuit module is joined with the bare cell, the slopeportion 59 may function to prevent the interference between the stepportion 56 and the wing portion 53 g.

According to the lead plates 50 a to 50 g of the aforementionedembodiments, the weight of the mounting portion may be greater than thatof the joint portion, so that it may be possible to prevent the jointportion from being inclined from the surface of the bare cell due to themovement of a centroid of the lead plate to the joint portion when theprotection circuit module is welded to the bare cell. That is, accordingto example embodiments, the welding strength of the lead plate may beincreased, so that it may be possible to prevent the lead plate frombeing collapsed or to prevent a welding portion from easily coming offby an impact applied to the corner portion of the battery pack in thedrop test.

FIGS. 11A and 11B illustrate perspective views of sequential processesin a method of manufacturing a battery pack according to an embodiment.Referring to FIGS. 11A and 11B, a protection circuit module 10 may beprepared. Here, the lead plate 50 and the dummy plate 51 may beconnected to the protection circuit module 10. The bare cell 100 mayalso be prepared.

The lead plate 50 and dummy plate 51 of the protection circuit module 10correspond to the lead plates described with reference to FIGS. 1A and1B. Each of the lead plate 50 and the dummy plate 51 may be replacedwith any one of the lead plates 50 a to 50 g of the aforementionedembodiments or a combination thereof.

The protection circuit module 10 may be laser-welded to the top surfaceof the bare cell 100. Welding points 140 may be formed on the lead plate50 and the dummy plate 51 by the laser welding. The top surface of thebare cell 100 corresponds to a side surface on which a negativeelectrode terminal 120 and an electrolyte injection hole 130 are formed.The electrolyte injection hole 130 may be sealed after an electrolyte isinjected into the bare cell 100 therethrough.

According to this embodiment, when the top surface of the bare cell 100is compressed by the protection circuit module 10 in the laser welding,the joint portion of each of the lead plate 50 and the dummy plate maynot be inclined or lifted from the top surface of the bare cell 100.Thus, the welding process may be stably performed.

The bare cell 100 may include a can type case 110, and an electrodeassembly (not shown) and an electrolyte (not shown) accommodated in thecase. A safety vent 112 for discharging an internal gas in an increaseof internal pressure may be formed at one side surface of the case 110.

The electrode assembly may be formed by using a stacked body or windingthe stacked body. Here, the stacked body may be formed by sequentiallystacking a positive electrode plate, a separator, and a negativeelectrode plate. The electrolyte assembly may have positive and negativeelectrode tabs respectively attached to the positive and negativeelectrode plates. The positive electrode tab may be electricallyconnected to the case 110, and the negative electrode tab may beelectrically connected to the electrode terminal 120. The electrolytemay be a solid polymer electrolyte or gel polymer electrolyte.

The positive electrode plate may have a sheet-shaped positive electrodecollector and a positive electrode active material coated on thepositive electrode collector. The negative electrode plate may have asheet-shaped negative electrode collector and a negative electrodeactive material coated on the negative electrode collector.

The positive electrode active material may include a transition metaloxide containing lithium, representative of metal oxides, e.g., LiCoO₂,LiNiO₂, LiMnO₂, LiMn₂O₄ and LiNi_(1-x-y)Co_(x)M_(y)O₂ (0≦x≦1, 0≦y≦1,0≦x+y≦1, and M is a metal, such as Al, Sr, Mg or La), or a lithiumchalcogenide compound. The negative electrode active material may be acarbon material, e.g., crystalline carbon, amorphous carbon, carboncomposite or carbon fiber, a lithium metal or a lithium alloy.

The positive and negative electrode collectors may be formed of one ormore of stainless steel, nickel, copper, aluminum and alloy thereof. Inorder to maximize efficiency, the positive electrode collector may beformed of aluminum or aluminum alloy, and the negative electrodecollector may be formed of copper or copper alloy.

The separator may be positioned between the positive and negativeelectrode plates. The separator may be formed to prevent an electricalshort circuit between the positive and negative electrode plates and toallow the movements of lithium ions. The separator may be formed of apolymer film, e.g., polyethylene (PE), polypropylene (PP), polyolefin,or a multi-layered film thereof.

The battery pack of this embodiment may include a holder frame forsupporting the protection circuit module 10 at one side of the bare cell100, a cover frame fixed to the holder frame while surrounding theprotection circuit module 10, and an outer label for surrounding thebare cell 100 and the holder frame. A water sensitive paper may beprovided to the cover frame.

According to example embodiments, in a protection circuit module or abattery pack having the same, it may be possible to enhance the jointstrength between a bare cell and the protection circuit module by usinga lead plate having a mounting portion that is heavier than the jointportion. Further, a joining process of the bare cell and the protectioncircuit module may be easily performed by a laser soldering method, andthe failure rate in the joining process may be decreased. Furthermore,the joint strength between the bare cell and the protection circuitmodule may be improved, thereby enhancing the drop reliability of thebattery pack. In addition, the joining between the bare cell and a leadplate, e.g., a nickel tab, serving as a current path of the protectioncircuit module may be improved, thereby enhancing the performance andreliability of the battery pack.

Exemplary embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation.Accordingly, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made without departingfrom the spirit and scope of the present invention as set forth in thefollowing claims.

What is claimed is:
 1. A secondary battery, comprising: a bare cell; aprotection circuit module on the bare cell; and a lead plate joined withthe protection circuit module, the lead plate including; a mountingportion connected to a printed circuit board (PCB) in the protectioncircuit module, a joint portion connected to the bare cell, the mountingportion being heavier than the joint portion, and a surface area of thejoint portion facing the bare cell being smaller than a surface area ofthe mounting portion facing the PCB, and a step portion connecting themounting portion and the joint portion to each other.
 2. The secondarybattery as claimed in claim 1, wherein the mounting portion includes acontact region and a non-contact region, the contact region contacting asurface of the PCB, and a surface area of the contact region beingsmaller than the surface area of the joint portion facing the bare cell.3. The secondary battery as claimed in claim 2, wherein the non-contactregion of the mounting portion extends away from the contact region. 4.The secondary battery as claimed in claim 2, wherein the non-contactregion has a wing portion bent and extended outward from the contactregion.
 5. The secondary battery as claimed in claim 4, wherein a lengthof the wing portion is shorter than that of the step portion.
 6. Thesecondary battery as claimed in claim 4, wherein a width of the wingportion decreases in a direction extending outward from the mountingportion, the wing portion being spaced apart from the step portion at apredetermined interval.
 7. The secondary battery as claimed in claim 1,wherein a first boundary portion between the mounting portion and thestep portion and a second boundary portion between the step portion andthe joint portion are bent, at least one of the first and secondboundary portions including a notch.
 8. The secondary battery as claimedin claim 1, wherein the mounting portion includes a first portion havinga first thickness and a second portion having a second thicknessdifferent than the first thickness, at least one of the first and secondportions of the mounting portion being thicker than the joint portion.9. The secondary battery as claimed in claim 1, wherein a width of themounting portion is larger than a width of the joint portion.
 10. Thesecondary battery as claimed in claim 1, wherein the joint portionincludes an opening.
 11. The secondary battery as claimed in claim 1,wherein the mounting portion and the joint portion directly contact thePCB and the bare cell, respectively, the PCB being parallel to an uppersurface of the bare cell, and the step portion extending at an angleother than 0° or 180° with respect to each of the PCB and the uppersurface of the bare cell to define a space between the PCB an the barecell.
 12. The secondary battery as claimed in claim 1, wherein theentire protection circuit module is external to the bare cell, the leadplate being between a lowermost surface of the protection circuit moduleand an uppermost surface of the bare cell, and the lowermost surface ofthe protection circuit module and the uppermost surface of the bare cellfacing opposite directions.
 13. The secondary battery as claimed inclaim 1, wherein the mounting portion is between the protection circuitmodule and the bare cell.
 14. A protection circuit module, comprising: aprinted circuit board (PCB); a safety element and an external connectionterminal on the PCB; and a lead plate joined with the PCB, the leadplate including: a mounting portion connected to the PCB, a jointportion connected to a bare cell, a surface area of the joint portionfacing the bare cell being smaller than a surface area of the mountingportion facing the PCB, and a step portion connecting the mountingportion and the joint portion to each other.
 15. The protection circuitmodule as claimed in claim 14, wherein the mounting portion includes acontact region and a non-contact region, the contact region contacting asurface of the PCB, and the surface area of the contact region beingsmaller than the surface area of the joint portion facing the bare cell.16. The protection circuit module as claimed in claim 14, wherein afirst boundary portion between the mounting portion and the step portionand a second boundary portion between the step portion and the jointportion are bent, and at least one of the first and second boundaryportions includes a notch.
 17. The protection circuit module as claimedin claim 14, wherein the mounting portion includes a first portionhaving a first thickness and a second portion having a second thicknessdifferent than the first thickness, at least one of the first and secondportions of the mounting portion being thicker than the joint portion.18. The protection circuit module as claimed in claim 14, wherein themounting portion is heavier than the joint portion.
 19. The protectioncircuit module as claimed in claim 14, wherein the step portion extendsat an angle other than 0° or 180° with respect to each of the PCB andthe bare cell to define a space between the PCB an the bare cell, thesafety element and external connection terminal being in the spacebetween the PCB an the bare cell.
 20. The protection circuit module asclaimed in claim 14, wherein the entire protection circuit module isexternal to the bare cell, the mounting portion being between theprotection circuit module and the bare cell.